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Whole Number Rounding

Achievement Objectives:

Achievement Objective: NA4-6: Know the relative size and place value structure of positive and negative integers and decimals to three places.
AO elaboration and other teaching resources

Specific Learning Outcomes: 

Identify and order decimals to three places.

Round whole numbers and decimals, with up to two places, to the nearest whole number, or tenth.

Description of mathematics: 

Number Framework Stage 7.

Required Resource Materials: 
whole Number Rounding (Material Master 8-11).

Whole number rounding is a gentle yet important introduction to using number lines to round decimal numbers sensibly.

Using Materials

Problem: “Betty’s Appliance Store prices TVs to the nearest $10. If the exact price is $567.78, what does Betty charge?”

Discuss why the choices are 560 and 570 and enter these at the end of the number line 10 units apart. Discuss why 567 is 7 divisions along from 560. Discuss why 567.78 is nearer 568 than 567 and locate 567.78 with an arrow on the number line.



Discuss why 567.78 ≈ 570 to the nearest 10.

Examples: Stories for rounding on number lines:
$456.89 to the nearest $10 $2,345.09 to the nearest $10
$7,456 to the nearest $100 $24,509 to the nearest $1,000

Using Imaging

Problem: “A builder works out the price of building a house as $123,566.89. He quotes a price to the nearest $1,000. What is his price?”

Discuss the two alternatives ($123,000 and $124,000). Ask the students to draw an empty number line (Material Master 8–11) and put 123 000 and 124 000 at the ends.  Ask where 123 500 would be on the number line. (Answer: Half way.) So is 123 566.89 closer to 123 000 or 124 000? (Answer: 124 000. So the builder charges $124,000.)

Examples: Stories for rounding on empty number lines:

$345,902.89 to the nearest $1,000 $266,345.09 to the nearest $100
$794,856.23 to the nearest $10,000 $5,624,509 to the nearest $100,000

Using Number Properties

Examples: Stories for rounding without number lines:

9 099.99 to the nearest 10 795.078 to the nearest 100
94 756.2309 to the nearest 10 000 999.999 to the nearest 1
11.89 to the nearest 1 10 890.8 to the nearest 100
956.2709 to the nearest 10 999 999.9 to the nearest 1


Understanding Number Properties:

A number rounds to 345 800 to the nearest hundred. What kind of number could it be?